In the field of vehicle suspensions, the phrase "quarter car suspension" refers to the components of the vehicle suspension relating to one of the four wheels of the typical automotive vehicle. These components include the particular wheel with a tire that is in contact with the road, a spring that transfers the road force to the vehicle body (sprung mass) and suspends the vehicle body, and a damper or actuator that reduces undesirable relative movement between the vehicle body and wheel. The complete suspension system of an automotive vehicle comprises four quarter car suspensions.
In recent years, vehicle manufacturers have dedicated significant effort to developing suspension systems responsive to the driving conditions of the vehicle. This effort is triggered by desire to incorporate the best features of soft and stiff suspension systems into a single vehicle suspension system. The best feature of a soft vehicle suspension is the smooth ride it provides for the vehicle passengers. The best feature of a stiff vehicle suspension is the increased handling performance it provides for the vehicle.
The theory of semi-active suspension systems is to selectively switch between stiff suspension and soft suspension in response to the particular driving conditions of the vehicle. Selection between stiff suspension and soft suspension may be obtained by altering the damping force of the suspension system, e.g., a greater damping force for a stiffer suspension and a lower damping force for a softer suspension. With correct control of suspension damping force, a vehicle can provide both optimum driving comfort and optimum handling performance. Semi-active suspension systems (along with active systems) can be referred to as variable force suspension systems.
Difficulties in designing variable force suspension systems lie partially in system controls. For example, the state of the suspension at each wheel of the vehicle is affected not only by road disturbance on the wheel, but by the rigid body characteristics of the vehicle body.
What is desired is a suitable system for integrating four semi-active suspension systems into a vehicle to provide optimum vehicle handling and ride comfort.